Regulation of Rainbow Trout Muscle Myofibrillar Networks by Non-Enzymatic Bioactive Compounds from Chaenomeles speciosa

During marination and boiling processes, structural rearrangement of muscle proteins plays an important role in determining the texture, water retention, and flavor quality of fish products. This study investigated the effects of Chaenomeles speciosa aqueous extract (SE), rich in non-enzymatic bioactive compounds, on the myofibrillar networks of rainbow trout muscle. The effects of SE on rainbow trout muscle quality were evaluated under marination and boiling conditions. SE treatment improved muscle tenderness, water-holding capacity, and flavor characteristics under both processing conditions. The hardness of boiled muscle decreased from 15.06 N in the control group to 6.03–8.29 N after SE treatment, while shear force decreased by 19–31% and 18–32% under marination and boiling conditions, respectively. The water-holding capacity of boiled muscle reached approximately 78–79% after treatment with SE at 80 mg/mL. Structural analyses, including low-field nuclear magnetic resonance and scanning electron microscopy, suggested that SE treatment was associated with changes in water distribution and the formation of a relatively looser and more flexible myofibrillar network, which may be related to alterations in protein conformation, surface hydrophobicity, and thiol–disulfide balance. Furthermore, low-to-moderate SE concentrations reduced key fishy odor-related compounds, with octanal decreasing by 70.2% in the SE-80-B group. Importantly, these effects were still observed after boiling, when protease activity was undetectable, suggesting that heat-stable non-enzymatic components of SE may play a role in modifying muscle protein organization beyond the effects of acidification or proteolysis. Overall, SE may serve as a potential natural ingredient for improving the processing quality of rainbow trout products.